1. Field of the Invention
The present invention relates to a dirty fluid sampling valve and more particularly to a dirty fluid sampling valve having a mechanical latching or detent system to secure the valve in an open or closed position. The mechanical latching system itself can be used in other types of two position valves to secure the valve in an open or closed position.
2. Description of the Prior Art
Dirty fluid sampling valves are designed for insertion into a valve chamber in the body of a downhole tool used for sampling wellbore fluids at varying depths. The typical downhole tool has approximately seven to ten sample collection bottles with a different dirty fluid valve connected to each bottle. Prior to insertion of the tool into the hole, the sample collection bottles are empty and all the dirty fluid valves are closed. The dirty fluid valves are then opened at various depths to sample different formation fluids within the well. Unfortunately, changes in pressure or shocks to the drill string may cause prior art valves to open prematurely, resulting in inaccurate sampling, or to open a second time, losing or contaminating the captured sample. A valve opening at the wrong depth destroys the value of the test. Improving the reliability of the dirty fluid valve is therefore important due to the high completion costs associated with oil and gas exploration. Completion of a hole at the wrong depth is a serious error that is tremendously difficult to correct.
The present patent application is assigned to Gilmore Valve Co. Since the early 1990""s, Gilmore Valve Co. has sold various types of dirty fluid valves (including drawing numbers 25080, 25081, 25085 ad 25086, copies of which are included with the INFORMATION DISCLOSURE STATEMENT filed concurrently herewith) without a mechanical latching or detent system. There is therefore a need for a mechanical latching system to improve the reliability of dirty fluid valves and the downhole test samples they control. Other art valves have attempted to overcome the problem of premature opening of the valve. Detenting mechanisms shown in the prior art generally involve detent grooves or holes on a piston that accept detent balls or a ring that is urged inwardly. Further, prior art detent systems generally secure the valve in, or urge the valve toward, only one position.
One such prior art valve is disclosed in U.S. Pat. No. 4,364,412 to Peters for a pull type relay valve with an automatic lockout. This valve utilizes pilot pressure actuation to lock the slide valve in position. The valve is sealed by O-rings on a piston. A compression spring is used within a piston channel to push against the piston to continuously urge the slide valve inwardly towards the closed or seated position. The valve is opened by manually pulling the slide valve to the set or opened position.
Another prior art valve is a control valve having a centering and detenting mechanism as disclosed in U.S. Pat. No. 4,260,132 to Habiger. The mechanism includes first and second coil springs disposed concentrically and in overlapping relationship relative to one another. A flange integral to a tubular retainer forms a stop surface to engage a piston and precisely position it within the retainer. A plurality of circumferentially spaced holes are formed through a tubular extension of the tubular retainer to mount ball-type detents. The detents are urged radially inwardly into seating engagement within the holes of the tubular extension.
The dirty fluid sampling valve of the present invention is adapted to be inserted in a valve chamber of a downhole tool for sampling wellbore fluids. The tool has at least one wellbore fluid inlet connected to at least one dirty fluid valve and at least one sample collection bottle. The tool has at least one wellbore fluid outlet so the collection bottle can be drained for laboratory analysis. The tool includes at least one open pilot to deliver open fluid to the valve, and at least one close pilot to deliver close fluid to the valve, as described below.
The valve has a valve body that defines pilot open and pilot close ports, as well as valve inlet and outlet ports. The inlet and outlet ports are in fluid communication with the inlet and outlet of the downhole tool. The valve body has a central bore which houses a piston, the piston being moveable between valve open and valve closed positions in response to pressure from the pilot open and pilot close ports.
The piston carries a seal assembly that blocks fluid communication between the valve inlet and outlet ports when the piston is in the valve closed position. The piston further includes a detent assembly which releasingly engages a first detent groove in the valve body when the piston is in the valve closed position and releasingly engages a second detent groove in the valve body when the piston is in the valve open position.
In a preferred embodiment, the detent assembly includes a c-ring that is engaged and urged outwardly by radially extending pins. The pins are urged outwardly by a ball bearing that is continuously biased by a spring carrier in combination with at least one belleville spring. The spring or springs are captured between the spring carrier and an adjusting nut that threadably engages the piston.
As the piston moves into the valve open or valve closed position, the c-ring is aligned with the corresponding detent groove. The belleville spring urges the spring carrier against the ball bearing to bias the pins against the detent ring, thereby urging the detent ring into the detent groove. Upon pressure sufficient to further compress the belleville spring, the detent ring compresses to disengage the detent groove allowing the piston to move within the central bore. This mechanical latching or detent system reduces the likelihood that the dirty fluid valve will unintentionally open or close.